HAL Portal ESPCI (Ecole Supérieure de Physique et de Chimie Industrielles)
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Targeting the cell membrane in established and emerging model organisms
No full textInternational audienceTransgenic markers and tools have revolutionised how we study cells and developing organisms.Some of the elements needed to construct those tools are universally applicable (e.g. fluorescentproteins), while others are species-specific (e.g. cis-regulatory elements driving transcription).Membrane-localising signals that target proteins to the plasma membrane have been identified inseveral model organisms. Unfortunately, the efficacy of these signals varies greatly across species. Toaddress this problem, we generated a toolkit of 11 membrane-localising tags that can be screenedrapidly in diverse organisms. The toolkit includes tags that target the plasma membrane throughdifferent mechanisms, including signal peptides, the attachment of lipids, and fusion withlipid-binding domains. Each tag has been fused to the red fluorescent protein mScarlet3 and placeddownstream of a T7 promoter, allowing the in vitro production of mRNA that can be readily deliveredin a wide range of embryos and cells of interest. Through a collaborative effort, we tested this toolkitin ten species of animals spanning diverse phyla, including chordates, echinoderms, arthropods,nematodes, annelids, flatworms and cnidarians. We identify robust membrane-localising tags in eachof these animals, and in one of animals' closest relatives, the choanoflagellates. Three tags (KRas,GAP43 and Src64B) work in all of the species tested
Photoaccumulation of Long‐Lived Reactive Electrons in a Microporous Ti(IV) Oxocluster‐Based Metal–Organic Framework for Light and Dark Photocatalysis
No full textInternational audienceAbstract The microporous Ti 12 oxocluster‐based metal–organic framework (MOF) MIP‐177(Ti)‐LT exhibits excellent stability and photoactivity, making it highly promising for photocatalysis. Using transient and photoinduced absorption spectroscopies, the behavior of reactive electrons in MIP‐177(Ti)‐LT across femtosecond‐to‐second timescales is investigated. The framework shows efficient charge separation and slow decay kinetics, with photogenerated charges persisting into the microsecond‐second (µs‐s) range and displaying higher yields and slower recombination than benchmark MOFs MIL‐125(Ti)‐NH 2 and UiO‐66(Zr)‐NH 2 . Photogenerated holes oxidize water with an O 2 yield of 335 µmol g −1 h −1 in the presence of electron scavengers. Under continuous irradiation, long‐lived electrons accumulate, further enhanced by a hole scavenger (methanol). Remarkably, these electrons persist over 48 h post‐excitation under argon, accompanied by a reversible white‐to‐black color change. The stored electrons remain redox‐active, efficiently reducing added O 2 and methyl viologen. Dark addition of a Pt co‐catalyst to photocharged MIP‐177(Ti)‐LT induces H 2 evolution at ≈300 µmol g −1 (≈58 C g −1 ), corresponding to an accumulated electron density of one electron per 12 Ti atoms. These results highlight the photocharging properties of MIP‐177(Ti)‐LT and its potential for sustainable photocatalytic applications
Optoretinography with Time-Domain Full-Field OCT: Achieving Cellular Resolution and Wide Field-of-View Functional Imaging
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Suivi de la plasticité cortico-striatale lors de la transition d’un comportement dirigé vers un but vers des stratégies habituelles
No full textThe aim of this PhD project was to better understand how learning-related plasticity emerges and evolves within the dorsal striatum during the acquisition of new skills. Motivated by this goal, we developed a novel behavioral paradigm to investigate the neural mechanisms underlying procedural learning by longitudinally tracking synaptic plasticity in corticostriatal circuits. Through head-fixed mice performing a self-paced task, combined with chronic in vivo recordings of Channelrhodopsin-2 evoked local field potentials (ChR2-eLFPs), we revealed a distinct spatial and temporal dissociation of plasticity within the dorsal striatum. Specifically, the dorsolateral striatum (DLS) displayed robust and sustained long-term potentiation (LTP) of cortical inputs across training, whereas the dorsomedial striatum (DMS) showed either stable responses or a gradual decline consistent with long-term depression. These opposing dynamics may not be purely epiphenomenal but also functionally significant: applying low-frequency stimulation to disrupt DLS-LTP appeared to impair both synaptic potentiation and behavioral performance, suggesting a possible contribution of DLS plasticity to skill acquisition and consolidation. Interestingly, following more detailed behavioral and correlation analyses, mice showing LTD in the DMS were among the best performers, supporting a framework in which DMS-LTD helps refine goal-directed behavior by suppressing outdated strategies and facilitating behavioral consistency. Whether animals develop automatic or habitual strategies during learning remains an open question, currently under investigation through more detailed behavioral analyses. Classical reward devaluation tests, commonly used to assess habitual control, have proven only partially informative in our task, likely due to high interindividual variability. To better characterize behavioral strategies, ongoing work combines refined behavioral metrics with dopamine fiber photometry aligned to licking behavior, which may offer a complementary approach to identify and cluster distinct learning profiles in mice.Altogether, these findings suggest a model in which procedural learning may involve region-specific and temporally distinct forms of corticostriatal plasticity, with DMS-LTD potentially contributing to the refinement of goal-directed behavior and DLS-LTP supporting the emergence of automaticity. This mechanistic dissociation enhances our understanding of how complex actions are acquired, consolidated, and optimized through dynamic cortical-striatal interactions.L’objectif de ce projet de thèse était de mieux comprendre comment la plasticité liée à l’apprentissage émerge et évolue au sein du striatum dorsal lors de l’acquisition de nouvelles compétences. Motivés par ce but, nous avons développé un nouveau paradigme comportemental afin d’étudier les mécanismes neuronaux sous-jacents à l’apprentissage procédural en suivant longitudinalement la plasticité synaptique dans les circuits corticostriataux. En entraînant des souris dans un dispositif qui les maintient par la tête à réaliser une tâche auto-initiée, et en combinant cela à des enregistrements in vivo chroniques de potentiels locaux évoqués par optogénétique (opto-eLFPs), nous avons mis en lumière une dissociation claire, à la fois spatiale et temporelle, de la plasticité au sein du striatum dorsal. Plus précisément, le striatum dorsolatéral (DLS) présent une potentialisation à long terme (LTP) robuste et soutenue des entrées corticales tout au long de l’entraînement, tandis que le striatum dorsomédial (DMS) montre soit des réponses stables, soit un déclin progressif cohérent avec une dépression à long terme (LTD). Ces dynamiques opposées ne sont probablement pas de simples épiphénomènes mais pourraient avoir une signification fonctionnelle : l’application d’une stimulation basse fréquence (LFS) pour perturber la LTP dans le DLS semble altérer à la fois la potentialisation synaptique et la performance comportementale, suggérant une possible contribution de la plasticité du DLS à l’acquisition et à la consolidation des compétences. Remarquablement, à la suite d’analyses comportementales et de corrélations plus détaillées, les souris montrant une LTD dans le DMS figuraient parmi les plus performantes, ce qui soutient un cadre dans lequel la LTD du DMS contribue à affiner le comportement orienté vers un but. La question de savoir si les animaux adoptent des stratégies automatiques au cours de l’apprentissage reste encore ouverte. Les tests classiques de dévaluation de la récompense, souvent utilisés pour évaluer l’émergence d’automatisme, se sont révélés peu informatifs dans notre paradigme comportemental en raison d’une importante variabilité interindividuelle des souris. Afin de mieux caractériser les stratégies comportementales, les travaux en cours associent les différents paramètres comportementaux à de la photométrie mesurant la dopamine. Cette approche pourrait permettre d’identifier et de regrouper différents profils d’apprentissage chez la souris. Dans l’ensemble, ces résultats appuient un modèle selon lequel l’apprentissage procédural repose sur des formes de plasticité corticostriatale à la fois spécifiques à certaines régions et distinctes dans le temps : la LTD dans le DMS contribuerait à affiner le comportement orienté vers un but, tandis que la LTP dans le DLS favoriserait l’émergence de l’automaticité. Cette dissociation fonctionnelle enrichit notre compréhension des processus par lesquels des actions complexes sont acquises, consolidées et optimisées au travers d’interactions dynamiques entre cortex et striatum
Deep-lying semi-Dirac fermions in hexagonal close-packed cadmium
No full textSemi-Dirac fermions are massless in one direction and massive in the perpendicular directions. Such quasiparticles have been proposed in various contexts in condensed matter. Using first principles calculations, we identify a pair of semi-Dirac bands anti-crossing at eV below the Fermi level in the electronic structure of hexagonal close-packed cadmium. The linear out-of-plane dispersion is kept up to the Fermi level. We demonstrate that the dichotomy between the linear and quadratic dispersions is driven by an orientation-sensitive hybridization between the and orbitals. The upper semi-Dirac band produces a lens-shaped nonellipsoidal Fermi sheet whose cross-section area has a -dependence that is in excellent agreement with the experimentally measured period of Sondheimer oscillations
Shadowgraphy measurements of bubble jet coupled with surface oscillations
No full textInternational audienceWe present an image processing method to track and characterize the motion of air–liquid interfaces occurring in aerated liquid baths. In a rectangular tank filled with water, an immersed sparger injects air vertically at a constant flow rate and creates well-defined sloshing oscillations of the free surface. The phenomenon is referred to as self-induced sloshing.We retrieve the positions of both the surface and the jet position using a tailored image processing method based on shadowgraphy. Using Complex Orthogonal Decomposition (COD), we reveal the main spatial and temporal dynamics of the oscillations
Photoaccumulation of Long-lived Reactive Electrons in the Microporous Ti(IV) Oxocluster Based Metal-organic Framework for Light and Dark Photocatalysis
No full textThe microporous Ti12 oxocluster based metal-organic framework MIP-177(Ti)-LT exhibits excellent stability and photoactivity, making it highly promising for photocatalytic applications (LT stands for low temperature synthesis). This study employs transient and photoinduced absorption spectroscopies to analyse the behaviour of reactive electrons in MIP-177(Ti)-LT across femtosecond-to-second timescales. Over these timescales, MIP-177(Ti)-LT shows effective charge separation and relatively slow decay kinetics, with photogenerated charges persisting through to microsecond-second timescales and exhibiting significantly higher yields and slower decay kinetics than two benchmark metal(IV) oxoclusters based photoactive MOFs, MIL-125(Ti)-NH2 and UiO-66(Zr)-NH2. Photogenerated holes in MIP-177(Ti)-LT are found to be able to oxidise water to produce oxygen at a yield of 335 µmol g-1⋅ h-1 in the presence of electron scavengers. Meanwhile, long-lived photogenerated electrons accumulate under continuous irradiation, with this accumulation being enhanced by the presence of a hole scavenger, methanol. Notably, these photogenerated electrons can persist for over 48 hours post-photoexcitation under sealed conditions in argon, causing a reversible colour shift from white to black. These accumulated long-lived electrons are shown to be redox-active, efficiently reducing both added oxygen and methyl-viologen. The subsequent dark addition of a platinum co-catalyst to the photocharged MIP-177(Ti)-LT results in hydrogen evolution with a yield of circa 300 µmol/g (~58 C/g), corresponding to an accumulated electron density of one electron per 12 Ti atoms (i.e., one electron per titania oxocluster). These results highlight the photocharging properties of MIP-177(Ti)-LT and its potential for sustainable and efficient photocatalytic processes
Compartmentalized Suspension Array for the Isothermal, Digital, and Multiplex Detection of microRNAs
No full textInternational audienceThe sensitive and accurate detection of panels of microRNA molecules is critical to enable their use as disease biomarkers. While microarrays and next-generation sequencing allow comprehensive miRNA profiling, they generally suffer from low accuracy and sensitivity. Conversely, digital bioassays such as digital PCR provide an absolute quantification with unrivaled sensitivity, although with limited multiplexing capabilities. In this work, we describe a novel microRNA profiling procedure, termed Digiplex, that combines the multiplexing power of a DNA-grafted suspension array with the accuracy of a digital flow cytometry readout. microRNAs are first captured on fluorescently encoded DNA-grafted particle populations following a Poisson distribution. The particles are subsequently isolated in microfluidic droplets, where single captured miRNA molecules trigger an isothermal exponential amplification that ultimately activates a fluorescent probe on the particle surface. Flow cytometry analysis yields the ratio of positive to negative particles for each targeted microRNA, allowing the reconstruction of the multiplex concentration profile in one go. After optimizing the workflow on a single microRNA model, we successfully developed a 10-plex assay with femtomolar sensitivity. The Digiplex method was finally validated on total RNA samples and benchmarked against droplet digital PCR
Experimental study of Su-Schrieffer-Heeger edge modes for water waves in linear and nonlinear regimes
No full textInternational audienceThis paper experimentally investigates topologically protected edge modes in a water wave channel through a direct geometric mapping to the one-dimensional Su-Schrieffer-Heeger (SSH) model. By designing a periodic channel with alternating widths, we replicate the key features of the SSH model, leading to the emergence of robust zero-energy sloshing edge modes localized at the boundaries. Experimental data show excellent agreement with theoretical predictions, supported by two-dimensional numerical simulations. In the nonlinear regime, two distinct bifurcations are observed, indicating the appearance of secondary resonances. This study highlights the relevance of the SSH model for water-wave systems and provides an accessible method to explore topological edge states in classical wave systems
Open channels and radiation trapping eigenstates in complex resonant media
No full textInternational audienceWe present a statistical study of the transmission and dwell-time matrices in disordered media composed of resonators, focusing on how frequency detuning influences their eigenvalue distributions. Our analysis reveals that the distribution of transmission eigenvalues undergoes a transition from a monomodal to a bimodal profile, and back to monomodal, as the frequency approaches the resonant frequency of the particles. Moreover, the distribution of dwell-time eigenvalues broadens significantly near resonance, with the longest lifetimes exceeding the median by several orders of magnitude. These results are explained by examining how frequency ω affects the transport mean free path of light ℓ ( ω ) and the energy transport velocity vE( ω ) , which in turn shape the observed distributions. We demonstrate the strong potential of wavefront shaping to synthesize wavefronts associated with eigenstates that enhance transmission and energy storage (or radiation trapping) in resonant disordered media. In the diffusive regime, where the system thickness L exceeds the mean free path, both transmission and dwell time can be enhanced by a factor ∝ L / ℓ(ω) ≫ 1 when using wavefronts associated with the largest eigenvalues instead of plane waves. In the localized regime, the enhancements become ∝ Ne2L/ξ for transmission and ∝ Nξ/L for dwell time, where ξ is the localization length and N is the number of controlled scattering channels. Finally, we show that employing high- Q resonators instead of low- Q ones increases energy storage within the medium by a factor of ∝ Q/kℓ(ω) in both the diffusive and localized regimes